A standard flush valve such as described in copending application Ser. No. 09/176,163 filed Oct. 21, 1998 has a valve ring defining a downwardly open valve port, an overflow tube centered on an upright axis and having a lower end opening into the valve port, and a valve body at the tube lower end displaceable relative to the port between a closed blocking position and an open position. Mechanism inside the tube lifts the valve body into the open position. A float in the tank adjacent the port cooperates with a latch system connected to the valve body for holding the body in the open position while the float is generally submerged. The tube is internally formed with an inwardly projecting ridge. The mechanism includes a frame inside the tube and fixed axially in the tank, at least one claw axially displaceable in the tube relative to the frame and engageable with the ridge, an actuating element accessible from outside the tank above the tube and axially aligned with the tube, and a direction-reversing linkage mounted on the frame and connected between the actuating element and the claw for raising the claw when the element is depressed.
Such a valve provides a standard full flush. It is however frequently desirable in order to conserve water to use substantially less than such a full flush.